Question

4. An Ideal diesel engine has a compression ratio of 20 and uses air as the working fluid. The state of air at the beginning of the compression process is 95kPa and 20°C. If the maximum temperature in the cycle is not to exceed 2200K, determine a) the thermal efficiency and b) the mean effective pressure. Assume constant specific heats for air at room temperature. 5. An aircraft engine operates on a simple ideal Brayton cycle with a pressure ratio of 10. Heat is added to the cycle at a rate of 500 KW; air passes through the engine at a rate of 1 kgs, and the air at the beginning of the compression is at 70 kPa and 0°C. Determine the power produced by this engine and its thermal efficiency. Use constant specific heats at room temperature. 6. A simple ideal Brayton Cycle operates with air with a minimum and maximum temperatures of 27°C and 727°C. It is designed so that the maximum cycle pressure is 2000 kPa and the minimum cycle pressure of 100 kPa. Determine the net work produced per unit mass of air each time this cycle is executed and the cycle's thermal efficiency. Use constant specific heats at room temperature. 7. A simple ideal Rankine Cycle which uses water as the working fluid operates its condenser at 40°C and its boiler at 250°C. Calculate the work produced by the turbine, the heat supplied in the boiler, and the thermal efficiency of this cycle when the steam enters the turbine without any superheating. 8. A steam power plant operates on an ideal reheat Rankine cycle between the pressure limits 15 MPa and 10 kPa. The mass flow rate of steam through the cycle is 12 kg/s. Steam enters both stages of the turbine at 500°C. If the moisture content of the steam at the exit of the low-pressure turbine is not to exceed 5 percent, determine a) the pressure at which reheating takes place b) the total rate of heat input in the boiler, and c) the thermal efficiency of the cycle. Also, show the cycle on a T-S diagram with respect to saturation lines. 9. A steam power plant operates on an ideal regenerative Rankine cycle. Steam enters the turbine at 6 MPa and 450°C and is condensed in the condenser at 20 kPa. Steam is extracted from the turbine at 0.4 MPa to heat the feedwater in an open feedwater heater. Water leaves the feedwater heater as a saturated liquid. Show the cycle on a T-S diagram and determine a) the network output per kilogram of steam flowing through the boiler and b) the thermal efficiency of the cycle.

Answer 1

Air Ang I working fluid 92= = 20 PIE 95kpa Ti= 206 = 2931 Tmax= 2200 K Now is we know isentropic so in diesel cycle compression ratio

Now Tz = Tilry T2= 293 (2034-1 Iz= 971-13k pz = a() e = 95(20)14 =6297.46 kPa Now At Compressor inlet PIV=MRTI Pidi=RT Vie RTI = 0-281x293 95 Vi= 0.8851 m3/kg R: 0.28 the hero ah

addation. Uz a los = 0; eest dz= 0.0442 holky Now for const Press, heat Pane e che V3 = 73 to the Is- Timar.de 2V2 P3 V3 Tz T3 ..{P=Ps 3 { 13 = Tant} Tz 83= 2200 x 0.0442 971.13 Uz = 0.1002 3/kg cut off ratio will be s Now 0.1002 0.0642 P= 2:26 Thermal efficiency Now of disel cycle is E non = (1 SS

1.U-1 14 Min. = I - (2:26) -1 14(2-26-1) Nm. = 1-. 12093 hth = I now a 0.6354 63.54.1 I . Ang Pressure will be Now Heat added et const Quad = Cp dT Qadd = Co (T3-Iz) Paddi = 10112200 - 971:13) Qadd = 124145 kg/kg Now. We Know - Whet What = Min.x dadd What = 0.635481241.15 What = 788.63 kJ/kg

- Swelt volume Vs for the cyck is - Vs=virve Vs = 0.8851-0.0442 Vs = 0.8408 m3/kg - Now we know Net work done Mean effective Pressure = swept volume MEP= What Vs MEP = 788.63 0.8409 MEP = 937.84 kPa - Ang So Thermal efficiency hin = 63.54%. mean effective Pression (MER) = 937.84 kPa